Page 232 - Boiler plant and distribution system optimization manual

Boiler Plant Calculations 217

SAVING ENERGY BY IMPROVING C2-C1
CONDENSATE RETURN Formula A = ———————— = 0.08
(C1 x C2)- C1
In this case there is no blowdown heat re-
C =Present cycles of concentration = 7
covery system and the challenge is to conserve l
C =Anticipated cycles of concentration = 14
energy by reducing the blow-down as much as 2
possible. There are several ways to do this such as
Figure 11-8 indicates a savings of 3.00 mil-
repairing system leaks, improve feedwater quali-
lion Btu per 100,000 lb of makeup reduction. With
ty and increasing cycles of concentration.
a cost of steam of $8.00 per million Btus, estimate
Calculate the savings possible in a plant ex-
the dollar savings.
porting 2 million pounds of 100 psig steam a day.
Existing Blowdown 280,000 lb/day
Savings = 18.75 x $8.00 x 3 = $450/day
Target Blowdown 160,000 lb/day
= $164,250/Yr
BR x H x C
$ Savings = ———————
V x %E CONDENSATE SYSTEM WATER LEAKS

BR = blowdown reduction lb (280,000 -16,000 = Situation: Leaks are developing in the steam and
120,000) condensate systems and the make-up water us-
H = Heat content of blowdown (100 psi) age has risen from 50,000 gallons to 750,000 gal-
H = h - h 5 lons per month. How much fuel is it costing to
1
heat make-up water?
h -heat in war leaving boiler as blowdown.
1
(100 psig – 309 Btu/lb)
Fuel is natural gas costing $5.00 per million
h -heat in makeup feedwater (60F - 28 Btu/lb) Btus.
5
= h h (309 – 28) = 281 Btu/lb Condensate weighs 8.34 pounds per gallon.
1 5
C = Cost of fuel $1.00/Gal Boiler efficiency 78%
V =Heating Value of Fuel (No.2 fuel – 140,000
Btu/lb) Makeup water 50F 18 Btu/lb
E = Boiler Efficiency - 80% Normal condensate
return 180F 148 Btu/lb
120,000 1h/day x 281 Btu/lb x $100/Gal
$Savings = —————————————————— Btu loss per pound of
140,000 Btu/Gal x .80 make-up 130 Btu/lb
Fuel energy to heat water
$Savings = $301/day
with boiler 80% eff 162.5 Btu/lb
$Savings = $109,865/yr
How much fuel are the system leaks costing?

REDUCING BLOWDOWN LOSSES BY 700,000 gallons x 8.34lb/gallon
INCREASING CYCLES OF CONCENTRATION = 5.81 million lb
5.81 x 162.5 Btu/lb
Example 1. A 300 psi boiler rated at 250,000 = 944 million Btus/month
pounds of steam per hour uses 50% make-up
water averaging 1,875,000 pounds a day. It is an- 944 MBtu/mo x 5.00
ticipated that the cycles of concentration can be = $4,720/mo
raised from 7 to 14. What will the savings be? $56,640/yr (plus chemicals & water costs)